Method for receiving wake up packet via wake up radio module in wireless LAN system and wireless terminal using same

ABSTRACT

A method for communication in a wireless LAN system according to an embodiment includes: receiving, by a first wireless terminal including a main radio module and a WUR module for receiving a wake-up packet modulated based on OOK scheme, the wake-up packet from a second wireless terminal based on the WUR module, wherein the wake-up packet includes first information indicating that a broadcast scheme is applied to the wake-up packet and second information for indicating the presence of a group addressed frame buffered by the second wireless terminal; and controlling, by the first wireless terminal, the main radio module such that the main radio module remains in a doze state until a predetermined wake-up time after reception of the wake-up packet.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2019/000521, filed on Jan. 14, 2019,which claims the benefit of U.S. Provisional Application No. 62/617,231,filed on Jan. 14, 2018, the contents of which are all herebyincorporated by reference herein in their entirety.

TECHNICAL FIELD

The present disclosure relates to wireless communication, and morespecifically, to a method for communication in a wireless LAN system anda wireless terminal using the same.

BACKGROUND ART

Discussion for a next-generation wireless local area network (WLAN) isin progress. In the next-generation WLAN, an object is to 1) improve aninstitute of electronic and electronics engineers (IEEE) 802.11 physical(PHY) layer and a medium access control (MAC) layer in bands of 2.4 GHzand 5 GHz, 2) increase spectrum efficiency and area throughput, 3)improve performance in actual indoor and outdoor environments such as anenvironment in which an interference source exists, a denseheterogeneous network environment, and an environment in which a highuser load exists, and the like.

An environment which is primarily considered in the next-generation WLANis a dense environment in which access points (APs) and stations (STAs)are a lot and under the dense environment, improvement of the spectrumefficiency and the area throughput is discussed. Further, in thenext-generation WLAN, in addition to the indoor environment, in theoutdoor environment which is not considerably considered in the existingWLAN, substantial performance improvement is concerned.

In detail, scenarios such as wireless office, smart home, stadium,Hotspot, and building/apartment are largely concerned in thenext-generation WLAN and discussion about improvement of systemperformance in a dense environment in which the APs and the STAs are alot is performed based on the corresponding scenarios.

DISCLOSURE Technical Problem

An object of the present disclosure is to provide a method forcommunication with enhanced performance in a wireless LAN system and awireless terminal using the same.

Technical Solution

A method for communication in a wireless LAN system according to thepresent embodiment includes: receiving, by a first wireless terminalincluding a main radio module and a WUR module for receiving a wake-uppacket modulated based on OOK scheme, the wake-up packet from a secondwireless terminal based on the WUR module, wherein the wake-up packetincludes first information indicating that a broadcast scheme is appliedto the wake-up packet and second information for indicating the presenceof a group addressed frame buffered by the second wireless terminal; andcontrolling, by the first wireless terminal, the main radio module suchthat the main radio module remains in a doze state until a predeterminedwake-up time after reception of the wake-up packet.

Advantageous Effects

According to an embodiment of the present disclosure, a method forcommunication with enhanced performance in a wireless LAN system and awireless terminal using the same are provided.

DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual diagram illustrating a structure of a wirelessLAN system.

FIG. 2 is a diagram illustrating an example of a PPDU used in an IEEEstandard.

FIG. 3 is a conceptual diagram illustrating an authentication andassociation procedure after scanning of an AP and an STA.

FIG. 4 is an internal block diagram of a wireless terminal receiving awake-up packet.

FIG. 5 is a conceptual diagram illustrating a method in which a wirelessterminal receives a wake-up packet and a data packet.

FIG. 6 shows an example of a format of a wake-up packet.

FIG. 7 shows a signal waveform of a wake-up packet.

FIG. 8 is a diagram for describing a procedure in which powerconsumption is determined according to a ratio of bit valuesconstituting binary sequence information.

FIG. 9 is a diagram illustrating a design process of a pulse with OOK.

FIG. 10 is a diagram illustrating a basic operation for a WUR STA.

FIG. 11 is a diagram illustrating an operation in which a wirelessterminal operating in a power save mode periodically wakes up in orderto receive a beacon frame in a wireless LAN system.

FIG. 12 is a diagram illustrating a structure of a wake-up packetaccording to an embodiment.

FIG. 13 is a diagram illustrating a structure of a frame control fieldof the wake-up packet according to an embodiment.

FIG. 14 is a diagram illustrating a structure of a subfield included ina frame control field of a wake-up packet broadcast addressed accordingto an embodiment.

FIG. 15 is a flowchart illustrating a method for communication in awireless LAN system according to an embodiment.

FIG. 16 is a diagram illustrating a procedure for communication in awireless LAN system according to an embodiment.

FIG. 17 is a diagram illustrating a GID allocation procedure accordingto an embodiment.

FIG. 18 is a diagram illustrating a structure of a wake-up packet for aplurality of WUR STAs according to an embodiment.

FIG. 19 is a diagram illustrating a WUR ID/user bitmap according to anembodiment.

FIG. 20 is a diagram illustrating a WUR ID/user bitmap according toanother embodiment.

FIG. 21 is a diagram illustrating a structure of a wake-up packet for aplurality of WUR STAs according to another embodiment.

FIG. 22 is a block diagram illustrating a wireless device to which thepresent embodiment is applicable.

DETAILED DESCRIPTION

The above-described features and the following detailed description areexemplary contents for helping a description and understanding of thepresent specification. That is, the present specification is not limitedto this embodiment and may be embodied in other forms. The followingembodiments are merely examples to fully disclose the presentspecification, and are descriptions to transfer the presentspecification to those skilled in the art. Therefore, when there areseveral methods for implementing components of the presentspecification, it is necessary to clarify that the present specificationmay be implemented with a specific one of these methods or equivalentthereof.

In the present specification, when there is a description in which aconfiguration includes specific elements, or when there is a descriptionin which a process includes specific steps, it means that other elementsor other steps may be further included. That is, the terms used in thepresent specification are only for describing specific embodiments andare not intended to limit the concept of the present specification.Furthermore, the examples described to aid the understanding of thepresent specification also include complementary embodiments thereof.

The terms used in the present specification have the meaning commonlyunderstood by one of ordinary skill in the art to which the presentspecification belongs. Terms commonly used should be interpreted in aconsistent sense in the context of the present specification. Further,terms used in the present specification should not be interpreted in anidealistic or formal sense unless the meaning is clearly defined.Hereinafter, embodiments of the present specification will be describedwith reference to the accompanying drawings.

FIG. 1 is a conceptual diagram illustrating a structure of a WLANsystem. FIG. 1(A) illustrates a structure of an infrastructure networkof institute of electrical and electronic engineers (IEEE) 802.11.

Referring to FIG. 1(A), a WLAN system 10 of FIG. 1(A) may include atleast one basic service set (hereinafter, referred to as ‘BSS’) 100 and105. The BSS is a set of access points (hereinafter, APs) and stations(hereinafter, STAs) that can successfully synchronize and communicatewith each other and is not a concept indicating a specific area.

For example, a first BSS 100 may include a first AP 110 and one firstSTA 100-1. A second BSS 105 may include a second AP 130 and one or moreSTAs 105-1 and 105-2.

The infrastructure BSSs 100 and 105 may include at least one STA, APs110 and 130 for providing a distribution service, and a distributionsystem (DS) 120 for connecting a plurality of APs.

The DS 120 may connect a plurality of BSSs 100 and 105 to implement anextended service set (hereinafter, ‘ESS’) 140. The ESS 140 may be usedas a term indicating one network to which at least one AP 110 and 130 isconnected through the DS 120. At least one AP included in one ESS 140may have the same service set identification (hereinafter, SSID).

A portal 150 may serve as a bridge for connecting a WLAN network (IEEE802.11) with another network (e.g., 802.X).

In a WLAN having a structure as illustrated in FIG. 1(A), a networkbetween the APs 110 and 130 and a network between APs 110 and 130 andSTAs 100-1, 105-1, and 105-2 may be implemented.

FIG. 1(B) is a conceptual diagram illustrating an independent BSS.Referring to FIG. 1(B), a WLAN system 15 of FIG. 1(B) may performcommunication by setting a network between STAs without the APs 110 and130, unlike FIG. 1(A). A network that performs communication by settinga network even between STAs without the APs 110 and 130 is defined to anad-hoc network or an independent basic service set (hereinafter, ‘BSS’).

Referring to FIG. 1(B), an IBSS 15 is a BSS operating in an ad-hoc mode.Because the IBSS does not include an AP, there is no centralizedmanagement entity. Therefore, in the IBSS 15, STAs 150-1, 150-2, 150-3,155-4, and 155-5 are managed in a distributed manner.

All STAs 150-1, 150-2, 150-3, 155-4, and 155-5 of the IBSS may beconfigured with mobile STAs, and access to a distributed system is notallowed. All STAs of the IBSS form a self-contained network.

The STA described in the present specification is a random functionmedium including a medium access control (hereinafter, MAC) following astandard of the Institute of Electrical and Electronics Engineers (IEEE)802.11 standard and a physical layer interface for a wireless medium andmay broadly be used as a meaning including both an AP and a non-APstation (STA).

The STA described in the present specification may also be referred toas various names such as a mobile terminal, a wireless device, awireless transmit/receive unit (WTRU), a user equipment (UE), a mobilestation (MS), a mobile subscriber unit, or simply a user.

FIG. 2 is a diagram illustrating an example of a PPDU used in an IEEEstandard.

As illustrated in FIG. 2, various types of PHY protocol data units(PPDUs) may be used in a standard such as IEEE a/g/n/ac, etc. In detail,LTF and STF fields include a training signal, SIG-A and SIG-B includecontrol information for a receiving station, and a data field includesuser data corresponding to a PSDU.

The present embodiment proposes an improved scheme for a signal (orcontrol information field) used for a data field of a PPDU. The signalmentioned in the present embodiment may be applied onto high efficiencyPPDU (HE PPDU) according to an IEEE 802.11ax standard. The signalmentioned in the present specification may be HE-SIG-A and/or HE-SIG-Bincluded in the HE PPDU. For example, the HE-SIG-A and the HE-SIG-B mayalso be respectively represented as SIG-A and SIG-B. However, the signalmentioned in the present specification is not necessarily limited to anHE-SIG-A and/or HE-SIG-B standard and may be applied to control/datafields having various names, which include control information in awireless communication system transferring user data.

In addition, the HE PPDU of FIG. 2 is an example of a PPDU for multipleusers. The HE-SIG-B may be included only when the PPDU is for multipleusers. The HE SIG-B may be omitted in a PPDU for a single user.

As illustrated, the HE-PPDU for multiple users (MUs) may include variousfields such as legacy-short training field (L-STF), legacy-long trainingfield (L-LTF), legacy-signal (L-SIG), high efficiency-signal A (HE-SIGA), high efficiency-signal-B (HE-SIG B), high efficiency-short trainingfield (HE-STF), high efficiency-long training field (HE-LTF), data field(alternatively, a MAC payload), and packet extension (PE). Each of thefields may be transmitted during an illustrated time period (that is, 4or 8 μs).

The PPDU used in the IEEE standard is mainly described as a PPDUstructure transmitted with a channel bandwidth of 20 MHz. The PPDUstructure transmitted with a bandwidth (e.g., 40 MHz and 80 MHz) widerthan the channel bandwidth of 20 MHz may be a structure in which linearscaling is applied to the PPDU structure used in the channel bandwidthof 20 MHz.

The PPDU structure used in the IEEE standard may be generated based on64 Fast Fourier Transforms (FTFs), and a cyclic prefix portion (CPportion) may be ¼. In this case, a length of an effective symbolinterval (or FFT interval) may be 3.2 us, a CP length may be 0.8 us, andsymbol duration may be 4 us (3.2 us+0.8 us) that adds the effectivesymbol interval and the CP length.

FIG. 3 is a conceptual view illustrating an authentication andassociation procedure after scanning of an AP and an STA.

Referring to FIG. 3, a non-AP STA may perform the authentication andassociation procedure with respect to one AP among a plurality of APswhich have completed a scanning procedure through passive/activescanning. For example, the authentication and association procedure maybe performed through 2-way handshaking.

FIG. 3(A) is a conceptual view illustrating an authentication andassociation procedure after passive scanning, and FIG. 3(B) is aconceptual view illustrating an authentication and association procedureafter active scanning.

The authentication and association procedure may be performed regardlessof whether the active scanning or the passive scanning is used. Forexample, APs 300 and 350 exchange an authentication request frame 310,an authentication response frame 320, an association request frame 330,and an association response frame 340 with the non-AP STAs 305 and 355to perform the authentication and association procedure.

More specifically, the authentication procedure may be performed bytransmitting the authentication request frame 310 from the non-AP STAs305 and 355 to the APs 300 and 350. The APs 300 and 350 may transmit theauthentication response frame 320 to the non-AP STAs 305 and 355 inresponse to the authentication request frame 310. An authenticationframe format is disclosed in IEEE 802.11 8.3.3.11.

More specifically, the association procedure may be performed when thenon-AP STAs 305 and 355 transmit the association request frame 330 tothe APs 300 and 305. The APs 300 and 350 may transmit the associationresponse frame 340 to the non-AP STAs 305 and 355 in response to theassociation request frame 330.

The association request frame 330 may include information on capabilityof the non-AP STAs 305 and 355. The APs 300 and 350 may determinewhether the non-AP STAs 305 and 355 can be supported based on theinformation on capability of the non-AP STAs 305 and 355 and included inthe association request frame 330.

For example, if the support is available, the AP 300 and 350 maytransmit to the non-AP STAs 305 and 355 by allowing the associationresponse frame 340 to contain whether the association request frame 330is acceptable, its reason, and its supportable capability information.An association frame format is disclosed in IEEE 802.11 8.3.3.5/8.3.3.6.

When up to the association procedure mentioned in FIG. 3 is performed,normal data transmission and reception procedures may be performedbetween the AP and the STA.

FIG. 4 is an internal block diagram of a wireless terminal receiving awake-up packet.

Referring to FIG. 4, a WLAN system 400 according to the presentembodiment may include a first wireless terminal 410 and a secondwireless terminal 420.

The first wireless terminal 410 may include a main radio module 411related to main radio (e.g., 802.11 radio) and a WUR module 412including low-power wake-up radio (LP WUR). In the presentspecification, the main radio module may be referred to as a primarycomponent radio (hereinafter, PCR) module.

For example, the main radio module 411 may include a plurality ofcircuits supporting Wi-Fi, Bluetooth® radio (hereinafter, BT radio), andBluetooth® Low Energy radio (hereinafter, BLE radio).

In the present specification, the first wireless terminal 410 maycontrol the main radio module 411 in an awake state or a doze state.

For example, when the main radio module 411 is in the awake state, thefirst wireless terminal 410 is able to transmit an 802.11-based frame(e.g., 802.11-type PPDU) or receive an 802.11-based frame based on themain radio module 411. For example, the 802.11-based frame may be anon-HT PPDU of a 20 MHz band.

For another example, when the main radio module 411 is in the dozestate, the first wireless terminal 410 is not able to transmit the802.11-based frame (e.g., 802.11-type PPDU) or receive the 802.11-basedframe based on the main radio module 411.

That is, when the main radio module 411 is in the doze state (e.g., OFFstate), the first wireless terminal 400 is not able to receive a frame(e.g., 802.11-type PPDU) transmitted by the second wireless terminal 420(e.g., AP) until the WUR module 412 wakes up the main radio module 411to transition to the awake state according to a wake-up packet(hereinafter, WUP).

In the present specification, the first wireless terminal 410 maycontrol the WUR module 412 in the turn-off state or the turn-on state.

For example, the first wireless terminal 410 including the WUR module412 in the turn-on state is able to receive (or demodulate) only aspecific-type frame (i.e., WUR PPDU) transmitted by the second wirelessterminal 420 (e.g., AP).

In this case, the specific-type frame (e.g., WUR PPDU) may be a frame(e.g., wake-up packet) modulated by an on-off keying (OOK) modulationscheme described below with reference to FIG. 5.

For example, the first wireless terminal 410 including the WUR module412 in the turn-off state is not able to receive (or demodulate) aspecific-type frame (e.g., WUR PPDU) transmitted by the second wirelessterminal 420 (e.g., AP).

In the present specification, the first wireless terminal 410 canoperate a main radio module (i.e., PCR module 411) and a WUR module 412.

For example, when the main radio module 411 is in a power save mode(hereinafter referred to as a PS mode)), the first wireless terminal 410can control the main radio module 411 such that it alternates between adoze state and an awake state according to communication environment.

For example, when the WUR module 412 is in a WUR mode, the firstwireless terminal 410 can control the WUR module 412 such that italternates between a turn-on state and a turn-off state according to astate of the main radio module 411 and a duty cycle schedule agreed inadvance for the WUR module.

Here, a wake-up packet modulated with OOK can be received based on theWUR module 412 in a turn-on state. In other words, the wake-up packetcannot be received based on the WUR module 412 in a turn-off state.

Specifically, when the main radio module 411 is in a doze state, thefirst wireless terminal 410 in a WUR mode controls the WUR module 412such that it is in a turn-on state for a duty cycle schedule agreedbetween the first wireless terminal 410 and the second wireless terminal420.

Further, when the main radio module 411 is in an awake-state, the firstwireless terminal in the WUR mode may control the WUR module 412 suchthat it is in a turn-off state.

That is, a wireless terminal in the WUR mode may be understood as awireless terminal having a negotiation status between an AP and a WURSTA, in which the WUR module alternates between a turn-of state and aturn-off state when the main radio module is in a doze state.

For example, the first wireless terminal 410 in the WUR mode can receivea wake-up packet (WUP) based on the WUR module 412 in a turn-on state.Further, when the WUR module 412 receives a WUP, the first wirelessterminal 410 in the WUR mode can control the WUR module 412 such that itwakes the main radio module 411 up.

In the present specification, the terms “awake state” and “turn-onstate” may be interchanged in order to indicate an ON state of aspecific module included in a wireless terminal. In the same context,the terms “doze state” and “turn-off state” may be interchanged in orderto indicate an OFF state of a specific module included in a wirelessterminal.

The first wireless terminal 410 according to the present embodiment canreceive a legacy frame (e.g., a PPDU based on 802.11) from anotherwireless terminal 420 (e.g., AP) based on the main radio module 411 orthe WUR module 412 in an awake state.

The WUR module 412 may be a receiver for switching the main radio module411 in a doze state to an awake state. That is, the WUR module 412 maynot include a transmitter.

The first wireless terminal 410 can operates the WUR module 412 in aturn-on state for a duration in which the main radio module 411 is in adoze state.

For example, when a WUP is received based on the WUR module 412 in aturn-on state, the first wireless terminal 410 can control the mainradio module 411 in a doze state such that it switches to an awakestate.

For reference, a low power wake-up receiver (LP WUR) included in the WURmodule 412 aims at target power consumption of less than 1 mW. Further,the LP WUR may use a narrow bandwidth of less than 5 MHz.

In addition, power consumption of the LP WUR may be less than 1 Mw.Further, a target transmission range of the LP WUR may be the same asthat of the legacy 802.11.

The second wireless terminal 420 according to the present embodiment cantransmit user data based on main radio (i.e., 802.11). The secondwireless terminal 420 can transmit a WUP for the WUR module 412.

In the present specification, when a wireless terminal includes the mainradio module and the WUR module, the wireless terminal may be referredto as a WUR STA.

FIG. 5 is a conceptual diagram illustrating a method in which a wirelessterminal receives a wake-up packet and a data packet.

Referring to FIG. 4 and FIG. 5, a WLAN system 500 according to thepresent embodiment may include a first wireless terminal 510corresponding to a receiving terminal and a second wireless terminal 520corresponding to a transmitting terminal.

A basic operation of the first wireless terminal 510 of FIG. 5 may beunderstood through a description of the first wireless terminal 410 ofFIG. 4. Similarly, a basic operation of the second wireless terminal 520of FIG. 5 may be understood through a description of the second wirelessterminal 420 of FIG. 4.

Referring to FIG. 5, the wake-up packet 521 may be received in a WURmodule 512 in a turn-on state (e.g., ON state).

In this case, the WUR module 512 may transfer a wake-up signal 523 to amain radio module 511 in a doze state (e.g., OFF state) in order toaccurately receive a data packet 522 to be received after the wake-uppacket 521.

For example, the wake-up signal 523 may be implemented based on aninternal primitive of the first wireless terminal 510.

For example, when the wake-up signal 523 is received in the main radiomodule 511 in the doze state (e.g., OFF state), the first wirelessterminal 510 may control the main radio module 511 to transition to theawake state (i.e., ON state).

For example, when the main radio module 511 transitions from the dozestate (e.g., OFF state) to the awake state (i.e., ON state), the firstwireless terminal 510 may activate all or some of a plurality ofcircuits (not shown) supporting Wi-Fi, BT radio, and BLE radio includedin the main radio module 511.

For another example, actual data included the wake-up packet 521 may bedirectly transferred to a memory block (not shown) of a receivingterminal even if the main radio module 511 is in the doze state (e.g.,OFF state).

For another example, when an IEEE 802.11 MAC frame is included in thewake-up packet 521, the receiving terminal may activate only a MACprocessor of the main radio module 511. That is, the receiving terminalmay maintain a PHY module of the main radio module 511 to be in aninactive state. The wake-up packet 521 of FIG. 5 will be described belowin greater detail with reference to the accompanying drawings.

The second wireless terminal 520 may be configured to transmit thewake-up packet 521 to the first wireless terminal 510.

Referring to FIG. 5, to indicates that an individually addressedframe(s) for the first wireless terminal 510 is available through themain radio module 511 (i.e., to indicate the presence of an individuallyaddressed frame(s) buffered by the second wireless terminal for thefirst wireless terminal), the second wireless terminal 520 can transmita wake-up packet 521 to the first wireless terminal 510 associated withthe second wireless terminal 520.

For example, the wake-up packet 521 may include information (e.g., a WURID) for identifying the first wireless terminal 510.

Alternatively, the wake-up packet 521 may include information (e.g., agroup ID) for identifying a group of a plurality of wireless terminalsincluding the first wireless terminal 510.

Alternatively, the wake-up packet 521 may include a plurality of piecesof identification information in a frame body field. Here, the pluralityof pieces of identification information may include one for identifyingthe first wireless terminal 510.

FIG. 6 illustrates an example of a WUR PPDU format.

Referring to FIGS. 1 to 6, a wakeup packet 600 may include at least onelegacy preamble 610. In addition, the wake-up packet 600 may include apayload 620 after the legacy preamble 610. The payload 620 may bemodulated by a simple modulation scheme (e.g., On-Off Keying (OOK)modulation scheme). The wakeup packet 600 including a payload may betransmitted based on a relatively small bandwidth.

Referring to FIGS. 1 to 6, the second wireless terminal (e.g., 520) maybe configured to generate and/or transmit wakeup packets 521 and 600.The first wireless terminal (e.g., 510) may be configured to process thereceived wakeup packet 521.

For example, the wake-up packet 600 may include any other preamble (notshown) or a legacy preamble 610 defined in the existing IEEE 802.11standard. The wakeup packet 600 may include one packet symbol 615 afterthe legacy preamble 610. Further, the wake-up packet 600 may include apayload 620.

The legacy preamble 610 may be provided for coexistence with a legacySTA. An L-SIG field for protecting a packet may be used in the legacypreamble 610 for the coexistence.

For example, an 802.11 STA may detect a start portion of a packetthrough the L-STF field in the legacy preamble 610. The STA may detectan end portion of the 802.11 packet through the L-SIG field in thelegacy preamble 610.

In order to reduce false alarm of the 802.11n terminal, one modulatedsymbol 615 may be added after the L-SIG of FIG. 6. One symbol 615 may bemodulated according to a BPSK (BiPhase Shift Keying) scheme. One symbol615 may have a length of 4 us. One symbol 615 may have a 20 MHzbandwidth as a legacy part.

The legacy preamble 610 may be understood as a field for a third partylegacy STA (STA not including LP-WUR). In other words, the legacypreamble 610 may not be decoded by the LP-WUR.

FIG. 7 illustrates a signal waveform of a wake-up packet.

Referring to FIG. 7, a wake-up packet 700 may include a legacy preamble(802.11 preamble) 710 and payloads 722 and 724 modulated based on on-offkeying (OOK) scheme. That is, the wake-up packet WUP according to thepresent embodiment may be understood in a form in which a legacypreamble and a new LP-WUR signal waveform coexist.

OOK may not be applied to the legacy preamble 710 of FIG. 7. Asdescribed above, the payloads 722 and 724 may be modulated according tothe OOK. However, the wake-up preamble 722 included in the payloads 722and 724 may be modulated according to another modulation scheme.

For example, it may be assumed that the legacy preamble 710 istransmitted based on a channel band of 20 MHz to which 64 FFTs areapplied. In this case, the payloads 722 and 724 may be transmitted basedon a channel band of about 4.06 MHz.

FIG. 8 is a diagram illustrating a procedure in which power consumptionis determined according to a ratio of bit values constituting binarysequence information.

Referring to FIG. 8, binary sequence information having ‘1’ or ‘0’ as abit value may be expressed. Communication according to the OOKmodulation scheme may be performed based on a bit value of the binarysequence information.

For example, when a light emitting diode is used for visible lightcommunication, if the bit value constituting binary sequence informationis ‘1’, the light emitting diode may be turned on, and if the bit valueis ‘0’, the light emitting diode may be turned off.

As the receiving device receives and restores data transmitted in theform of visible light according to flickering of the light emittingdiode, communication using visible light is enabled. However, becausethe human eye cannot recognize flickering of the light emitting diode,the person feels that the lighting is continuously maintained.

For convenience of description, as shown in FIG. 8, binary sequenceinformation having 10 bit values may be provided. For example, binarysequence information having a value of ‘1001101011’ may be provided.

As described above, when the bit value is ‘1’, the transmitting terminalis turned on, and when the bit value is ‘0’, the transmitting terminalis turned off, and thus symbols corresponding to 6 bit values of theabove 10 bit values are turned on.

Because the wake-up receiver WUR according to the present embodiment isincluded in the receiving terminal, transmission power of thetransmitting terminal may not be largely considered. The reason why theOOK is used in this embodiment is that power consumed in a decodingprocess of the received signal is very small.

Until the decoding procedure is performed, there may be no significantdifference between power consumed by the main radio and power consumedby the WUR. However, as a decoding procedure is performed by thereceiving terminal, a large difference may occur between power consumedin the main radio module and power consumed in the WUR module. Below isapproximate power consumption.

-   -   Existing Wi-Fi power consumption is about 100 mW. Specifically,        power consumption of Resonator+Oscillator+PLL (1500 uW)->LPF        (300 uW)->ADC (63 uW)->decoding processing (Orthogonal        frequency-division multiplexing (OFDM) receiver) (100 mW) may        occur.    -   However, WUR power consumption is about 1 mW. Specifically,        power consumption of Resonator+Oscillator (600 uW)->LPF (300        uW)->ADC (20 uW)->decoding processing (Envelope detector) (1 uW)        may occur.

FIG. 9 is a diagram illustrating a design process of a pulse accordingto OOK.

A wireless terminal according to the present embodiment may use anexisting orthogonal frequency-division multiplexing (OFDM) transmitterof 802.11 in order to generate pulses according to OOK. The existing802.11 OFDM transmitter may generate a 64-bit sequence by applying64-point IFFT.

Referring to FIG. 1 to FIG. 9, the wireless terminal according to thepresent embodiment may transmit a payload of a modulated wake-up packet(WUP) according to OOK. The payload (e.g., 620 of FIG. 6) according tothe present embodiment may be implemented based on an ON-signal and anOFF-signal.

The OOK may be applied for the ON-signal included in the payload (e.g.,620 of FIG. 6) of the WUP. In this case, the ON-signal may be a signalhaving an actual power value.

With reference to a frequency domain graph 920, an ON-signal included inthe payload (e.g., 620 of FIG. 6) may be obtained by performing IFFT forthe N2 number of subcarriers (N2 is a natural number) among the N1number of subcarriers (N1 is a natural number) corresponding to achannel band of the WUP. Further, a predetermined sequence may beapplied to the N2 number of subcarriers.

For example, a channel band of the wakeup packet WUP may be 20 MHz. TheN1 number of subcarriers may be 64 subcarriers, and the N2 number ofsubcarriers may be 13 consecutive subcarriers (921 in FIG. 9). Asubcarrier interval applied to the wakeup packet WUP may be 312.5 kHz.

The OOK may be applied for an OFF-signal included in the payload (e.g.,620 of FIG. 6) of the WUP. The OFF-signal may be a signal that does nothave an actual power value. That is, the OFF-signal may not beconsidered in a configuration of the WUP.

The ON-signal included in the payload (620 of FIG. 6) of the WUP may bedetermined (i.e., demodulated) to a 1-bit ON-signal (i.e., ‘1’) by theWUR module (e.g., 512 of FIG. 5). Similarly, the OFF-signal included inthe payload may be determined (i.e., demodulated) to a 1-bit OFF-signal(i.e., ‘0’) by the WUR module (e.g., 512 of FIG. 5).

A specific sequence may be preset for a subcarrier set 921 of FIG. 9. Inthis case, the preset sequence may be a 13-bit sequence. For example, acoefficient corresponding to the DC subcarrier in the 13-bit sequencemay be ‘0’, and the remaining coefficients may be set to ‘1’ or ‘−1’.

With reference to the frequency domain graph 920, the subcarrier set 921may correspond to a subcarrier whose subcarrier indices are ‘−6’ to‘+6’.

For example, a coefficient corresponding to a subcarrier whosesubcarrier indices are ‘−6’ to ‘−1’ in the 13-bit sequence may be set to‘1’ or ‘−1’. A coefficient corresponding to a subcarrier whosesubcarrier indices are ‘1’ to ‘6’ in the 13-bit sequence may be set to‘1’ or ‘−1’.

For example, a subcarrier whose subcarrier index is ‘0’ in the 13-bitsequence may be nulled. All coefficients of the remaining subcarriers(subcarrier indexes ‘−32’ to ‘−7’ and subcarrier indexes ‘+7’ to ‘+31’),except for the subcarrier set 921 may be set to ‘0’.

The subcarrier set 921 corresponding to consecutive 13 subcarriers maybe set to have a channel bandwidth of about 4.06 MHz. That is, power bysignals may be concentrated at 4.06 MHz in the 20 MHz band for thewake-up packet (WUP).

According to the present embodiment, when a pulse according to the OOKis used, power is concentrated in a specific band and thus there is anadvantage that a signal to noise ratio (SNR) may increase, and in anAC/DC converter of the receiver, there is an advantage that powerconsumption for conversion may be reduced. Because a sampling frequencyband is reduced to 4.06 MHz, power consumption by the wireless terminalmay be reduced.

An OFDM transmitter of 802.11 according to the present embodiment mayhave may perform IFFT (e.g., 64-point IFFT) for the N2 number (e.g.,consecutive 13) of subcarriers of the N1 number (e.g., 64) ofsubcarriers corresponding to a channel band (e.g., 20 MHz band) of awake-up packet.

In this case, a predetermined sequence may be applied to the N2 numberof subcarriers. Accordingly, one ON-signal may be generated in a timedomain. One bit information corresponding to one ON-signal may betransferred through one symbol.

For example, when a 64-point IFFT is performed, a symbol having a lengthof 3.2 us corresponding to a subcarrier set 921 may be generated.Further, when a cyclic prefix (CP, 0.8 us) is added to a symbol having alength of 3.2 us corresponding to the subcarrier set 921, one symbolhaving a total length of 4 us may be generated, as in the time domaingraph 910 of FIG. 9.

Further, the OFDM transmitter of 802.11 may not transmit an OFF-signal.

According to the present embodiment, a first wireless terminal (e.g.,510 of FIG. 5) including a WUR module (e.g., 512 of FIG. 5) maydemodulate a receiving packet based on an envelope detector thatextracts an envelope of a received signal.

For example, the WUR module (e.g., 512 of FIG. 5) according to thepresent embodiment may compare a power level of a received signalobtained through an envelope of the received signal with a predeterminedthreshold level.

If a power level of the received signal is higher than a thresholdlevel, the WUR module (e.g., 512 of FIG. 5) may determine the receivedsignal to a 1-bit ON-signal (i.e., ‘1’). If a power level of thereceived signal is lower than a threshold level, the WUR module (e.g.,512 of FIG. 5) may determine the received signal to a 1-bit OFF-signal(i.e., ‘0’).

Generalizing contents of FIG. 9, each signal having a length of K (e.g.,K is a natural number) in the 20 MHz band may be transmitted based onconsecutive K subcarriers of 64 subcarriers for the 20 MHz band. Forexample, K may correspond to the number of subcarriers used fortransmitting a signal. Further, K may correspond to a bandwidth of apulse according to the OOK.

All coefficients of the remaining subcarriers, except for K subcarriersamong 64 subcarriers may be set to ‘0’.

Specifically, for a one bit OFF-signal corresponding to ‘0’(hereinafter, information 0) and a one bit ON-signal corresponding to‘1’ (hereinafter, information 1), the same K subcarriers may be used.For example, the used index for the K subcarriers may be expressed as33-floor (K/2): 33+ceil (K/2)−1.

In this case, the information 1 and the information 0 may have thefollowing values.

-   -   Information 0=zeros (1, K)    -   Information 1=alpha*ones (1, K)

The alpha is a power normalization factor and may be, for example,1/sqrt (K).

FIG. 10 illustrates a basic operation for a WUR STA.

Referring to FIG. 10, an AP 1000 may correspond to the second wirelessterminal 520 of FIG. 5. A horizontal axis of the AP 1000 of FIG. 10 mayindicate a time ta. A vertical axis of the AP 1000 of FIG. 10 may berelated to presence of a packet (or frame) to be transmitted by the AP1000.

A WUR STA 1010 may correspond to the first wireless terminal 510 of FIG.5. The WUR STA 1010 may include a main radio module (or PCR#m) 1011 anda WUR module (or WUR#m) 1012. The main radio module 1011 of FIG. 10 maycorrespond to the main radio module 511 of FIG. 5.

Specifically, the main radio module 1011 may support both a receptionoperation for receiving an 802.11-based packet from the AP 1000 and atransmission operation for transmitting the 802.11-based packet to theAP 1000. For example, the 802.11-based packet may be a packet modulatedaccording to an OFDM scheme.

A horizontal axis of the main radio module 1011 may indicate a time tm.An arrow displayed at the lower end of the horizontal axis of the mainradio module 1011 may be related to a power state (e.g., ON state or OFFstate) of the main radio module 1011.

The WUR module 1012 in FIG. 10 may correspond to the WUR module 512 inFIG. 5. Specifically, the WUR module 1012 can support only an operationof receiving packets modulated with on-off keying (OOK) from the AP1000.

A horizontal axis of the WUR module 1012 may indicate a time tw. Anarrow indicated at the lower end of the horizontal axis of the WURmodule 1012 may be related to a power state (e.g., ON state or OFFstate) of the WUR module 1012.

The WUR STA 1010 in FIG. 10 may be understood as a wireless terminalassociated with the AP 1000 through an association procedure.

The WUR STA 1010 in FIG. 10 may be understood as a wireless terminaloperating in the PS mode. Accordingly, the WUR STA 1010 can control themain radio module 1011 such that it is in a doze state or an awakestate.

Further, the WUR STA 1010 may be understood as a wireless terminaloperating in the WUR mode. Accordingly, the WUR STA 1010 can control theWUR module 1012 such that it is in a turn-off state or a turn-on state.

Referring to FIG. 5 and FIG. 10, the AP 1000 of FIG. 10 may correspondto the second wireless terminal 520 of FIG. 5. A horizontal axis of theAP 1000 of FIG. 10 may represent a time ta. A vertical axis of the AP1000 of FIG. 10 may be related to presence of a packet (or frame) to betransmitted by the AP 1000.

The WUR STA 1010 may correspond to the first wireless terminal 510 ofFIG. 5. The WUR STA 1010 may include a main radio module (or PCR#m) 1011and a WUR module (or WUR#m) 1012. The main radio module 1011 of FIG. 10may correspond to the main radio module 511 of FIG. 5.

Specifically, the main radio module 1011 may support both a receptionoperation for receiving an 802.11-based packet from the AP 1000 and atransmission operation for transmitting an 802.11-based packet to the AP1000. For example, the 802.11-based packet may be a packet modulatedaccording to the OFDM scheme.

A horizontal axis of the main radio module 1011 may represent a time tm.An arrow displayed at the lower end of the horizontal axis of the mainradio module 1011 may be related to a power state (e.g., ON state or OFFstate) of the main radio module 1011.

A vertical axis of the main radio module 1011 may be related to presenceof a packet to be transmitted based on the main radio module 1011. A WURmodule 1012 of FIG. 10 may correspond to the WUR module 512 of FIG. 5.Specifically, the WUR module 1012 may support only a reception operationfor a packet modulated from the AP 1000 according to OOK.

A horizontal axis of the WUR module 1012 may represent a time tw.Further, an arrow displayed at the lower end of the horizontal axis ofthe WUR module 1012 may be related to a power state (e.g., ON state orOFF state) of the WUR module 1012.

In a wake-up period TW to T1 in FIG. 10, the WUR STA 1010 can controlthe main radio module 1011 such that it is in a doze state (i.e., OFFstate). Further, the WUR STA 1010 can control the WUR module 1012 suchthat it is in a turn-on state (i.e., ON state).

When a data packet for the WUR STA 1010 exists in the AP 1000, the AP1000 may transmit a wake-up packet (WUP) to the WUR STA 1010 in acontention-based manner.

In this case, the WUR STA 1010 may receive the WUP based on the WURmodule 1012 in a turn-on state (i.e., ON state). Herein, the WUP may beunderstood based on the description mentioned above with reference toFIG. 5 to FIG. 7.

In a first duration T1 to T2 of FIG. 10, a wake-up signal (e.g., 523 ofFIG. 5) for waking up the main radio module 511 according to the WUPreceived in the WUR module 1012 may be transferred to the main radiomodule 511.

In the present specification, a time required when the main radio module511 transitions from a doze state to an awake state according to thewake-up signal (e.g., 523 of FIG. 5) may be referred to as a turn-ondelay (hereinafter, TOD).

Referring to FIG. 10, the main radio module 511 may be in an awake stateafter a lapse of the turn-on delay (TOD).

For example, upon elapse of the TOD, the WUR STA 1010 may control themain radio module 1010 to be in the awake state (e.g., ON state). Forexample, upon elapse of a wake-up duration TW to T1, the WUR STA 1010may control the WUR module 1012 to be in the turn-on state (i.e., OFFstate).

Subsequently, the WUR STA 1010 may transmit a power save poll(hereinafter, PS-poll) to the AP 1000 based on the main radio module1011 in the awake state (i.e., ON state).

Here, a PS-poll frame may be a frame for indicating that the WUR STA1010 can receive a data packet for the WUR STA 1010 present within theAP 1000 based on the main radio module 1011. Further, the PS-poll framemay be a frame transmitted based on contention with another wirelessterminal (not shown).

Subsequently, the AP 1000 may transmit a first ACK frame ACK#1 to theWUR STA 1010 in response to a PS-poll frame.

Subsequently, the AP 1000 may transmit a data packet for the WUR STA1010 to the WUR STA 1010. In this case, the data packet for the WUR STA1010 may be received based on the main radio module 1011 in an awakestate (i.e., ON state).

Subsequently, the WUR STA 1010 may transmit a second ACK frame ACK#2 fornotification of successful reception of the data packet for the WUR STA1010 to the AP 1000.

FIG. 11 is a diagram illustrating an operation in which a wirelessterminal operating in a power save mode periodically wakes up in orderto receive a beacon frame in a wireless LAN system.

For clear understanding of FIG. 11, a first STA 1110 and a second STA1120 may be assumed to be wireless terminals associated with an AP 1100through the association procedure of FIG. 3. In this case, the first STA1110 and the second STA 1120 need to periodically interact with the APin order to maintain association with the AP 1100.

Referring to FIG. 11, a first beacon frame transmitted at a first timeT1 may include delivery traffic indication map (DTIM) informationidentified by a DTIM count field set to “0” in TIM information.

For example, when the first bit Bit 0 of a partial virtual bitmap forthe DTIM information is set to “1”, this can indicate that groupaddressed traffic is available.

In the present disclosure, group addressed traffic can be understood asa frame transmitted by an AP based on a broadcast technique. Forexample, group addressed traffic buffered by the AP 1100 can bedelivered following the first beacon frame including the DTIMinformation.

For example, the first STA 1100 in an awake state can receive the firstbeacon frame including the DTIM information at the first time T1.Subsequently, the first STA 1100 can maintain the awake state in orderto receive group addressed traffic.

For example, a second beacon frame transmitted at a second time T2 ofFIG. 11 may include a DTIM count field set to “2” in TIM information.

Here, the DTIM count field set to “2” can indicate that there are twobeacon frames including TIM information before a beacon frame includingthe next DTIM information.

For clear understanding of FIG. 10, it is assumed that the second beaconframe indicates the presence of individually addressed traffic for thefirst STA 1110 and the second STA 1120.

In the case of FIG. 10, the first STA 1110 and the second STA 1120 cancheck TIM information at the second time T2 of FIG. 11 because both thefirst STA 1110 and the second STA 1120 are in an awake state in order toreceive the second beacon frame.

Subsequently, the first STA 1110 and the second STA 1120 may transmit aPS-Poll frame to the AP 1100 in order to poll traffic individuallybuffered by the AP 1100 for the first STA 1110 and the second STA 1120.

In the present disclosure, an interval (e.g., T1 to T1′ in FIG. 11)between beacon frames including DTIM information may be referred to as aDTIM interval. Further, a time (e.g., T1 and T1′ in FIG. 11) at which abeacon frame including DTIM information is transmitted may be referredto as a DTIM target beacon transmission time (TBTT). Referring to FIG.11, an interval (e.g., T1 to T2 in FIG. 11) having a specific duration(e.g. 100 ms) between beacon frames may be referred to as a beaconinterval.

FIG. 12 is a diagram illustrating a structure of a wake-up packetaccording to an embodiment.

Referring to FIGS. 1 to 12, a payload field (e.g., 620 in FIG. 6)included in a wake-up packet according to the present embodiment mayconforms to a MAC frame structure 1200.

The MAC frame structure 1200 of FIG. 12 may include a plurality offields 1210 to 1250. A frame control field 1210 is represented as 8-bitinformation B0-B7 and will be described in more detail with reference toFIG. 13.

An ID field 1220 may be represented as 12-bit information B8-B19. Forexample, when the wake-up packet is individually addressed,identification information (WUR identifier (WUR ID)) for a singlewireless terminal receiving a wake-up packet to which a unicast schemehas been applied may be set to the ID field 1220.

Specifically, the WUR ID included in the wake-up packet to which aunicast scheme has been applied may be used to identify a WUR STAintended to perform instantaneous response.

As another example, when a wake-up packet is group addressed, a group ID(GID) for a plurality of wireless terminals receiving a wake-up packetto which a multicast scheme has been applied may be set to the ID field1220.

Furthermore, when a wake-up packet is broadcast addressed,identification information (transmitter ID (TXID)) of a wirelessterminal transmitting a wake-up packet to which a broadcast scheme hasbeen applied may be set to the ID field 1220.

As another example, “0” may be set to the ID field 1220 in order tosignal that a plurality of WUR IDs is included in a frame body (1240 ofFIG. 12) of a wake-up packet.

A type dependent control field 1230 may be represented as 12-bitinformation B20-B31. For example, the type dependent control field 1230may include information related to BSS update.

A frame body field 1240 may have a variable length. The frame body field1240 may include WUR IDs for a plurality of wireless terminals.

A frame check sequence (FCS) field 1250 may include 16-bit CRCinformation.

FIG. 13 is a diagram illustrating a structure of a frame control fieldof a wake-up packet according to an embodiment.

Referring to FIG. 13, the frame control field 1300 (for example, 1210 ofFIG. 12) of a wake-up packet according to the present embodiment mayinclude a plurality of fields 1310 to 1350.

For clear and concise understanding of the present disclosure, it isassumed that the type field 1310 includes information for indicating awake-up packet. For example, the type field 1210 may have a 3-bitlength.

The length present field 1320 may include information for indicatingwhether a subsequent field 1330 includes a length subfield. For example,the length present field 1320 may have a 1-bit length.

The length/mist field 1330 may include a subfield in response toinformation included in the length present field 1320. For example, whenthe length/mist field 1330 includes a length subfield, the lengthsubfield can indicate the length of the frame body field (e.g., 1240 ofFIG. 12).

The protected field 1340 may include information indicating whetherinformation transmitted through the wake-up packet is processed by amessage integrity check (MIC) algorithm.

FIG. 14 is a diagram illustrating a structure of a subfield included ina frame control field of a broadcast addressed wake-up packet.

For clear and concise understanding of FIG. 14, it may be assumed thatidentification information (i.e., TXID) of a wireless terminaltransmitting a wake-up packet is included in the ID field 1220. Further,it may be assumed that the type field 1310 includes information forindicating the wake-up packet.

Referring to FIG. 14, a length/mist field 1400 (1330 of FIG. 13) mayinclude a 1-bit group addressed bufferable unit (BU) subfield 1410 (B0)and a 2-bit reserved field 1420 (B1-B2).

The group address BU subfield 1410 may include information for signalingthat an AP buffers one or more group addressed BUs.

FIG. 15 is a flowchart illustrating a method for communication in awireless LAN system according to an embodiment.

Referring to FIGS. 1 to 15, a first wireless terminal can be understoodas a wake-up radio (WUR) STA including a main radio module and a WURmodule for receiving a wake-up packet modulated based on on-off keying(OOK) scheme. In addition, a second wireless terminal can be understoodas an AP.

The first wireless terminal may receive a wake-up packet (WUP) from thesecond wireless terminal based on the WUR module in step S1510.

For example, the wake-up packet may include first information indicatingthat a broadcast scheme is applied. Here, the first information may beidentification information (i.e., TXID) of the AP that transmits thewake-up packet. For example, the TXID may be included in an ID field(e.g., 1220 of FIG. 12) having a 12-bit length.

For example, the wake-up packet may include second information forsignaling the presence of a group addressed frame (e.g., a broadcastframe) buffered by the second wireless terminal. For example, the secondinformation may be included in a group addressed BU subfield (e.g., 1410of FIG. 14) having a 1-bit length.

The first wireless terminal may control the main radio module such thatthe main radio module remains in a doze state until a predeterminedwake-up time in step S1520.

For example, the wake-up time may be determined according to a powersaving (PS) operation agreed in advance between the first wirelessterminal and the second wireless terminal. Further, the wake-up time maycorrespond to a target beacon transmission time (TBTT) includingdelivery traffic indication map (DTIM) information.

The first wireless terminal may control the main radio module such thatthe main radio module switches to an awake state at the wake-up time instep S1530.

The first wireless terminal may receive a beacon frame from the secondwireless terminal based on the main radio module in the awake state instep S1540. In this case, the beacon frame may include DTIM information.

The first wireless terminal may receive a group addressed frame (e.g., abroadcast frame) from the second wireless terminal after reception ofthe beacon frame including the DTIM information in step S1550.

FIG. 16 is a diagram illustrating a procedure for communication in awireless LAN system according to an embodiment.

Referring to FIGS. 1 to 6, an AP 1600 of FIG. 16 can be associated witha first WUR STA 1610 and a second WUR STA 1620. The first WUR STA 1610and the second WUR STA 1620 of FIG. 16 may be understood as wirelessterminals operating based on a PS operation.

The first WUR STA 1610 of FIG. 16 may include a first main radio module1611 (PCR#m1) for receiving a legacy packet based on IEEE 802.11 and afirst WUR module 1612 (WUR#m1) for receiving a packet modulated based onOOK scheme.

Similarly, the second WUR STA 1610 may include a second main radiomodule 1621 (PCR#m2) and a second WUR module 1622 (WUR#m2).

The AP 1600 can transmit a wake-up packet WUP in a wake-up interval TWto T1.

For example, the wake-up packet WUP may be a packet to which a broadcastscheme has been applied. In this case, the wake-up packet may includefirst identification information (i.e., TXID) of the AP 1600.

Further, the wake-up packet WUP may include second identificationinformation (i.e., 1410 of FIG. 14) for signaling the presence of agroup addressed frame (e.g., a broadcast data frame) buffered by the AP1600.

In the present disclosure, the second identification information may bereferred to as a broadcast addressed frame indication information.

The first WUR STA 1610 may control the first main radio module 1611(PCR#m1) such that the first main radio module 1611 is in a turn-onstate (i.e., ON state) in the wake-up interval TW to T1. Similarly, thesecond WUR STA 1620 may control the second WUR module 1622 such that thesecond WUR module 1622 is in a turn-on state (i.e., ON state) in thewake-up interval TW to T1.

For reference, the first main radio module 1611 may be in a doze stateor an awake state in the wake-up interval TW to T1 of FIG. 16.Similarly, the second main radio module 1621 may be in a doze state oran awake state.

In a first interval T1 to T2, the first WUR STA 1610 may control thefirst main radio module 1611 such that the first main radio module 1611to be in a doze state until a predetermined wake-up time (e.g., T2 ofFIG. 16).

Similarly, in the first interval T1 to T2, the second WUR STA 1620 maycontrol the second main radio module 1621 such that the second mainradio module 1621 to be in a doze state until the predetermined wake-uptime (e.g., T2 of FIG. 16).

For example, the wake-up time (e.g., T2 of FIG. 16) may be determinedaccording to a PS operation type agreed in advance between the firstwireless terminal and the second wireless terminal.

In addition, the wake-up time (e.g., T2 of FIG. 16) may correspond to atarget beacon transmission time (TBTT) including delivery trafficindication map (DTIM) information.

At the starting time T2 of a second interval T2 to T3, the first WUR STA1610 may control the first main radio module 1611 such that the firstmain radio module 1611 switches to an awake state. Similarly, at thestarting time T2 of the second interval T2 to T3, the second WUR STA1620 may control the second main radio module 1621 such that the secondmain radio module 1621 switches to an awake state.

The first WUR STA 1610 may receive a beacon frame from the AP 1600 basedon the first main radio module 1611 in the awake state in the secondinterval T2 to T3.

Similarly, the second WUR STA 1620 may receive the beacon frame from theAP 1600 based on the second main radio module 1621 in the awake state inthe second interval T2 to T3.

In this case, the beacon frame may be a broadcast frame including DTIMinformation.

The first WUR STA 1610 and the second WUR STA 1620 may receive a groupaddressed frame (e.g., a broadcast data frame) buffered by the AP 1600in the remaining period of the second interval T2 to T3.

In this case, the group addressed frame (e.g., a broadcast data frame)buffered by the AP 1600 may be received based on the first main radiomodule 1611 and the second main radio module 1621.

FIG. 17 is a diagram illustrating a GID allocation procedure accordingto an embodiment.

Referring to FIG. 17, a WUR STA may be a wireless terminal that isassociated with an AP by performing a procedure of associating with theAP in advance. That is, the WUR STA may be a wireless terminal havingunique association identifier (AID) information in a BSS of the AP.

In step S1710, the STA may transmit a WUR mode suspend request frame tothe AP.

In step S1720, the STA may receive a WUR mode suspend response framefrom the AP in response to the WUR mode suspend request frame.

In step S1730, the STA may receive a WUR GID management frame from theAP. In this case, the WUR GID management frame may include one or morepieces of GID information for the STA.

In step S1740, the STA may transmit a WUR mode request frame to the AP.

In step S1750, the STA may receive a WUR mode response frame from the APin response to the WUR mode request frame.

For example, a wake-up packet to which a multicast scheme has beenapplied (hereinafter, multicast wake-up packet) may be used fortransmission of multicast-group addressed frames and transmission of aPCR module based MU PPDU (e.g., unicast data).

In general, the AP may not request that the intended STA transmit a WURresponse frame in response to a multicast wake-up packet formulticast-group addressed frames.

In the present disclosure, when a multicast wake-up packet istransmitted for transmission of a PCR module based MU PPDU (e.g.,unicast data), a mechanism of indicating whether the intended STAtransmits a WUR response frame in response to the multicast wake-uppacket may be required.

For example, a 1-bit indicator may be added to the control field of themulticast wake-up packet. In this case, whether the AP requests a WURresponse frame from the intended STA can be identified using the 1-bitindicator.

Alternatively, two types of GID for multicast wake-up packettransmission may be defined. That is, a first type of GID may be used torequest a WUR response frame from the intended STA and a second type ofGID may be used in order not to request the WUR response frame from theintended STA.

For example, the WUR response frame may be a PS-Poll frame or a QoS nullframe.

FIG. 18 is a diagram illustrating a structure of a wake-up packet for aplurality of WUR STAs according to an embodiment.

Referring to FIG. 18, the wake-up packet for a plurality of WUR STAs mayhave an extended format structure 1800 of a multicast wake-up packet.

The extended format structure 1800 of the multicast wake-up packet mayinclude information for the plurality of WUR STAs in a frame body field1820.

The extended format structure 1800 of the multicast wake-up packet ofFIG. 18 may include a plurality of fields 1810 to 1830.

For example, the MAC header 1810 of FIG. 18 may include type informationset to “1”, length information set to 2 bytes, and address informationset to GID.

For example, when the MAC header 1810 includes address information setto GID and length information having a value greater than “0”, as shownin FIG. 18, the frame body field 1820 may include WUR ID/user bitmapinformation.

Here, only at least one STA corresponding to a position set to “1” inthe WUR ID/user bitmap information in the frame body field 1820 can turnon a PCR module thereof.

Alternatively, when the MAC header 1810 includes address information setto GID and length information set to “0”, the frame body field 1820 maynot be present in the extended wake-up packet 1800.

Here, all STAs corresponding to a corresponding group can turn on theirPCR modules.

FIG. 19 is a diagram illustrating a WUR ID/user bitmap according to anembodiment.

Referring to FIGS. 18 and 19, a position of an STA in a WUR ID/userbitmap 1900 may be represented by a bit N(B_N). Here, a bit N may be avalue obtained by performing a modulo operation on the WUR ID of the STAbased on the size of the bitmap 1900.

For example, a position of an STA X in the WUR ID/user bitmap 1900 maybe B_3 obtained by performing a modulo operation on the WUR ID (“3”) ofthe STA X based on the size (“16”) of the bitmap 1900.

For example, a position of an STA Y in the WUR ID/user bitmap 1900 maybe B_0 obtained by performing a modulo operation on the WUR ID (“32”) ofthe STA Y based on the size (“16”) of the bitmap 1900.

For example, a GID included in a multicast wake-up packet may correspondto one of one or more GIDs allocated to the STA.

If the GID included in the multicast wake-up packet does not correspondto any GID for the STA, the multicast wake-up packet can be ignored. Forreference, the WUR ID/user bitmap may be implemented in various manners.

FIG. 20 is a diagram illustrating a WUR ID/user bitmap according toanother embodiment.

Referring to FIG. 20, when an AP allocates a GID to an STA, the AP maynotify the STA of a user position in a group. That is, user positioninformation may be added to a frame for GID allocation. In other words,the size of the user position information may depend on a maximum sizeof a user bitmap.

Referring to FIG. 20(A), when the maximum size of the user bitmap is 2bytes (i.e., 16 bits), 4 bits may be allocated for user positioninformation.

Referring to FIG. 20(B), when the maximum size of the user bitmap is 4bytes (i.e., 32 bits), 5 bits may be allocated for user positioninformation.

FIG. 21 is a diagram illustrating a structure of a wake-up packet for aplurality of WUR STAs according to another embodiment.

Referring to FIG. 21, the wake-up packet for a plurality of WUR STAs mayhave an extended format structure 2100 of a multicast wake-up packet.

The extended format structure 2100 of the multicast wake-up packet mayinclude information for a plurality of WUR STAs in a frame body field2120.

The extended format structure 2100 of the multicast wake-up packet ofFIG. 21 may include a plurality of fields 2110 to 2130.

For example, the MAC header 2110 of FIG. 21 may include type informationset to “1”, length information set to 6 bytes, and address informationin which GID is set to “0”.

Here, the address information in which GID is set to “0” may beunderstood as a value for indicating that a plurality of WUR IDs for aplurality of WUR STAB is included in a frame body.

FIG. 22 is a block diagram illustrating a wireless device to which thepresent embodiment is applicable.

Referring to FIG. 22, the wireless device is an STA that can implementthe above-described embodiment and may operate as an AP or a non-AP STA.Further, the wireless device may correspond to the aforementioned useror a transmitter that transmits a signal to the aforementioned user.

The wireless device of FIG. 22 includes a processor 2210, a memory 2220and a transceiver 2230 as shown. The processor 2210, the memory 2220 andthe transceiver 2230 may be implemented as separate chips or at leasttwo blocks/functions may be implemented as a single chip.

The transceiver 2230 includes a transmitter and a receiver, and only theoperation of any of the transmitter and the receiver or both operationsof the transmitter and the receiver may be performed when a specificoperation is performed. The transceiver 2230 may include one or moreantennas for transmitting and/or receiving RF signals. Further, thetransceiver 2230 may include an amplifier for amplifying a receivedsignal and/or a transmitted signal and a band pass filter fortransmission on a specific frequency band.

The processor 2210 may implement functions, processes and/or methodsproposed in the present disclosure. For example, the processor 2210 canperform operations according to the above-described embodiment. That is,the processor 2210 can perform operations disclosed in the embodiment ofFIGS. 1 to 21.

The processor 2210 may include an application-specific integratedcircuit (ASIC), other chipsets, logic circuits, a data processing deviceand/or a converter for converting a baseband signal and an RF signalinto each other. The memory 2220 may include a read-only memory (ROM), arandom access memory (RAM), a flash memory, a memory card, a storagemedium and/or other storage devices.

Although the present disclosure has been described with reference to theexemplary embodiments, those skilled in the art will appreciate thatvarious modifications and variations can be made in the presentdisclosure without departing from the scope of the disclosure describedin the appended claims. Accordingly, the present disclosure should notbe limited to the specific embodiments and the scope of the presentdisclosure should be determined by the appended claims and theirequivalents.

The invention claimed is:
 1. A method of communication in a wireless LAN system, comprising: receiving, by a first wireless terminal including a main radio module and a wake-up radio (WUR) module for receiving a wake-up packet modulated based on on-off keying (OOK) scheme, the wake-up packet from a second wireless terminal based on the WUR module, wherein the wake-up packet is received based on a broadcast scheme, and wherein the wake-up packet includes information on a presence of a group addressed frame buffered by the second wireless terminal; and controlling, by the first wireless terminal, the main radio module to remain in a doze state until a predetermined wake-up time after reception of the wake-up packet, wherein the wake-up packet further includes a user bitmap and information on a user position in a group indicated by the group identifier (GID), wherein at least one STA included in the first wireless terminal corresponding to the user position in the user bitmap set to 1 is transitioned from the doze state to an awake state at the predetermined wake-up time, and wherein a size of the information on the user position is determined based on a maximum size of the user bitmap.
 2. The method of claim 1, wherein the predetermined wake-up time is set by the first wireless terminal and the second wireless terminal.
 3. The method of claim 1, wherein the predetermined wake-up time relates to a target beacon transmission time (TBTT) including delivery traffic indication map (DTIM) information.
 4. The method of claim 3, further comprising: controlling, by the first wireless terminal, transition of the main radio module from the doze state to the awake state at the predetermined wake-up time; and receiving, by the first wireless terminal, a beacon frame from the second wireless terminal based on the main radio module in the awake state.
 5. The method of claim 4, further comprising: receiving, by the first wireless terminal, the group addressed frame from the second wireless terminal after reception of the beacon frame.
 6. A first wireless device performing a method for communication in a wireless LAN system, the first wireless device comprising: a transceiver for transmitting/receiving a radio frequency (RF) signal; and a processor connected to the transceiver, wherein the transceiver includes a main radio module and a wake-up radio (WUR) module for receiving a wake-up packet modulated based on on-off keying (OOK) scheme, and wherein the processor is configured to receive the wake-up packet from a second wireless terminal based on the WUR module and to control the main radio module to remain in a doze state until a predetermined wake-up time after reception of the wake-up packet, the wake-up packet is received based on a broadcast scheme is applied to the wake-up packet includes information on a presence of a group addressed frame buffered by the second wireless terminal, wherein the wake-up packet further includes a user bitmap and information on a user position in a group indicated by the group identifier (GID), wherein at least one STA included in the first wireless terminal corresponding to the user position in the user bitmap set to 1 is transitioned from the doze state to an awake state at the predetermined wake-up time, and wherein a size of the information on the user position is determined based on a maximum size of the user bitmap.
 7. The wireless terminal of claim 6, wherein the predetermined wake-up time is set by the first wireless terminal and the second wireless terminal.
 8. The wireless terminal of claim 6, wherein the predetermined wake-up time relates to a target beacon transmission time (TBTT) including delivery traffic indication map (DTIM) information.
 9. The wireless terminal of claim 8, wherein the processor is configured to control transition of the main radio module from the doze state to the awake state at the predetermined wake-up time and to receive a beacon frame from the second wireless terminal based on the main radio module in the awake state.
 10. The wireless terminal of claim 9, wherein the processor is configured to receive the group addressed frame from the second wireless terminal after reception of the beacon frame. 